1. Field
This application relates generally to improving network capacity in a wireless network.
2. Background
Unicast networks are typically optimized for unicast capacity in a serving cell. Since signals from adjacent cells are potentially interfering for systems such as long term evolution (LTE) and wideband code division multiple access (WCDMA), the base stations are configured to minimize interference of the service supporting cell as compared to a potentially interfering neighboring cell.
Among the techniques used to minimize unicast interference is down tilt. Down tilt refers to the angle of the peak of a main beam of a transmitted signal relative to the horizon. Multi-cast broadcast single frequency network (MBSFN) is a technique to enhance the received signal-to-noise ratio (SNR), and therefore the coverage or supported bit rate in a broadcast system. With single frequency network (SFN) transmissions, neighboring cells may transmit useful signals rather than signals that result in interference to the serving cell transmission. Because neighboring cells are co-operating rather than interfering, broadcast networks tend to operate with one or perhaps two degrees of down tilt, whereas the unicast networks are often operated with several more degrees of down tilt.
Multi-point unicast transmission has been introduced to enhance unicast performance. With multi-point transmission, multiple cells (including macros, picos and remote radio head (RRH), etc.) may coordinate with each other and transmit data jointly to the same user in a synchronized manner. In this case, the down tilt associated with joint transmission can be different (potentially decreased) from the down tilt for a unicast transmission sent from a single cell.
Some prior solutions utilize diurnal variation of down tilt within a unicast network. However, this sort of tilt variation is in general related to diurnal variation in traffic loading. A key aspect of this use of down tilt variation is the speed at which the variation of down tilt is accomplished. Specifically, the frequency of change for the typical diurnal variation is a few times each day. Accordingly, these solutions do not address transmissions in a wireless network where the frequency of change between a broadcast/unicast single frequency transmission and a unicast multi-point transmission TDM application may be many times per second.
Thus, improved network capacity in a wireless network is desired.